Scalable, Wasteless, and Energy-Efficient Diastereoselective Electrocatalytic Hydrogenation of Cyclic Ketones Using Proton-Exchange Membrane Reactor

We report the diastereoselective electrocatalytic hydrogenation of cyclic ketones using a proton-exchange membrane (PEM) reactor. Adsorbed monoatomic hydrogen species (Hads) generated from protons at the triple-phase boundary of the cathode were found to reduce the C=O bond of cyclic ketones with high diastereoselectivity; cis-selectivity as high as 94% was achieved under the optimal conditions using a Rh catalyst. Operando infrared (IR) spectroscopy enabled the direct observation of adsorbed ketones involved in the reaction. We also demonstrated the 5 g-scale electrolysis of 4-tert-butylcyclohexanone by combining the hydrogenation process with water oxidation as an anodic reaction. This reaction successfully produced cis-4-tert-butylcyclohexanol, which is 52 times more expensive than the starting material based on commercial prices, using only electric energy and water as reagents and, importantly, without H2 gas. This research demonstrates the potential of PEM reactors as reliable, robust, and green systems for the electrochemical production of fine chemicals.